The present invention relates generally to solenoid gas valves, and more particularly to a dual active pistons solenoid gas valve, in particular for alternative fuels vehicles.
In vehicles that run on gaseous alternative fuels, such as natural gas or hydrogen, the fuel is normally stored in a high-pressure tank, and a valve is utilized to open and close access to conduits, along which such high-pressure gaseous fluids flow from a storage tank to a vehicle engine. Typically such valves are of the solenoid type.
Solenoids of a reasonable size can typically produce a pulling force that is approximately only 1/100 of the force necessary to unseat a valve that is being forced shut by the high-pressure gasses. To overcome this, most of the gas valves adapt a two-stage process in which a small “bleed” orifice is first opened, allowing the high-pressure gas from the storage tank to flow through the “bleed” orifice and into a downstream outlet passage way that leads the engine. As the downstream outlet passage way fills up with gas, the pressure will increase, subsequently gradually reducing the force necessary to unseat the closed valve. Eventually, the differential pressure between the upstream and downstream passage ways becomes so small as to allow the valve to be open by the relatively weak pull of the solenoid valve, thus resulting in the flow of high-pressure gas from the storage tank to the vehicle engine.
One of the main problems with the above described system is the length of time required for the downstream chamber to fill with a sufficient volume of high-pressure gas, so that the solenoid can unseat the main valve. This problem is exasperated in large vehicles, such as buses where the gaseous fuel storage tank can be several meters away from the engine and therefore, it may take an unacceptable period of time for the passageway downstream of the valve to fill up to the point when the solenoid can unseat the main valve. These valves are also disadvantageous in vehicles that are bi-fueled by gasoline and natural gas or dual-fueled by diesel fuel and natural gas. When these vehicles switch over from liquid fuel to natural gas, there can be a conspicuous loss in power output over an unacceptable period of time, while the passage way downstream of the valve fills up with natural gas.